Lean burn combustor

ABSTRACT

A lean burn combustor includes a plurality of lean burn fuel injectors, each including a fuel feed arm and a lean burn fuel injector head with a lean burn fuel injector head tip, wherein the tip has a lean burn fuel injector head tip diameter, the lean burn fuel injector head including a pilot fuel injector and a main fuel injector, the main fuel injector being arranged coaxially and radially outwards of the pilot fuel injector; and a combustor chamber extending along an axial direction and including a radially inner annular wall, a radially outer annular wall, and a meter panel defining the size and shape of the combustor chamber, which includes a primary combustion zone with a primary combustion zone depth and a secondary combustion zone. A ratio of the primary combustion zone depth to the lean burn fuel injector head tip diameter is less than 2.4.

CROSS-REFERENCE TO RELATED APPLICATIONS

This specification is based upon and claims the benefit of priority fromUK Patent Application Number 2019219.1 filed on Dec. 7, 2020, the entirecontents of which are incorporated herein by reference.

BACKGROUND 1 Field of the Disclosure

The present disclosure relates to combustion equipment, and inparticular to lean burn combustors for gas turbine engines for aircraft,industrial, and marine applications.

2. Description of the Related Art

A gas turbine engine for aircraft applications typically comprises, inaxial flow arrangement, a fan, one or more compressors, a combustionsystem and one or more turbines. The combustion system typicallycomprises a plurality of fuel injectors having fuel spray nozzles whichcombine fuel and air flows and generate sprays of atomised liquid fuelinto a combustion chamber. The mixture of air and atomised liquid fuelis then combusted in the combustion chamber and the resultant hotcombustion products then expand through, and thereby drive, the one ormore turbines.

There is a continual need to reduce the environmental impact of gasturbine engines in terms of carbon emissions and nitrous oxides (NOx),which begin forming at high temperatures and increase exponentially withincreasing temperature.

In order to address the NOx emission issue, the “lean burn” combustiontechnology has been proposed. In lean burn combustion the air-to-fuelratio (AFR) is higher than a stoichiometric ratio, which allows to keepthe combustion temperature within limits known to reduce NOx production.

On the other hand, keeping the combustion temperature relatively lowcould lead to incomplete or weak combustion, which in turn may lead toproducing other pollutants, such as carbon monoxide (CO) and unburnedhydrocarbons (UHC), and/or flame instability and rumble, which in turnmay cause fatigue failure of components in the engine and/or passengerdiscomfort, depending on the frequency of the rumbling.

Gas turbine engines for industrial and marine applications face similarchallenges as gas turbine engines for aircraft applications.

There is therefore a need to provide a lean burn combustion system foraircraft, industrial, and marine engines which allows to reduce engineemissions of NOx, as well as CO and UHC, and improve engine operability.

SUMMARY

According to a first aspect, there is provided a lean burn combustorcomprising: a plurality of lean burn fuel injectors, each comprising afuel feed arm and a lean burn fuel injector head with a lean burn fuelinjector head tip, wherein the lean burn fuel injector head tip has alean burn fuel injector head tip diameter (d), the lean burn fuelinjector head comprising a pilot fuel injector and a main fuel injector,the main fuel injector being arranged coaxially and radially outwards ofthe pilot fuel injector; and a combustor chamber extending along anaxial direction and comprising a radially inner annular wall, a radiallyouter annular wall, and a meter panel provided upstream of the radiallyinner and radially outer annular walls with a plurality of aperturesadapted for accommodating the lean burn fuel injector head tips. Theradially inner annular wall, the radially outer annular wall, and themeter panel define the size and shape of the combustor chamber, whereinthe combustor chamber has a combustor chamber length (L) and comprises aprimary combustion zone with a primary combustion zone length (Z) and aprimary combustion zone depth (D), and a secondary combustion zone witha secondary combustion zone length (L-Z) arranged downstream of theprimary combustion zone. According to the first aspect, a ratio D/d ofthe primary combustion zone depth to the lean burn fuel injector headtip diameter is less than 2.4.

In the present disclosure, upstream and downstream are with respect tothe fuel and air flow through the combustor, and front and rear is withrespect to the lean burn combustor, i.e. the lean burn fuel injectorsbeing in the front and the combustor chamber being in the rear.

The present inventors have found a unique non-dimensional parametercombination for the combustor chamber that allows combustor aerodynamicsdeveloping to optimise combustion efficiency and minimise NOX and Smoke.The lean burn combustor according to the disclosure allows for aso-called S-shaped recirculation zone to form in the primary combustionzone of the combustor chamber, which allows the pilot fuel nozzle tosupport the main fuel nozzle combustion. In particular, the presentinventors have found that a combustor chamber according to thedisclosure allows the burning mixture of pilot fuel and air coming fromthe pilot fuel injector to form an S-shaped flow recirculation. Indetail, the burning mixture of pilot fuel and air coming from the pilotfuel injector may arrive at a stagnation point in the primary combustionzone, where the pilot fuel and air mixture local velocity is zero, gobackwards towards the lean burn fuel injectors, and be diverted (due tolow static pressure in the main flow stream) towards the radially innerand radially outer annular walls of the combustor chamber to join theburning mixture of main fuel and air coming from the main fuel injectorand support the combustion thereof. In other words, the burning mixtureof pilot fuel and air coming from the pilot fuel injector may flow alongan S-shaped trajectory.

The skilled person would appreciate that when designing a combustorchamber for a lean burn combustor, aerodynamics study have to be carriedout for any combustor chamber size in order to optimise the fuel and airmixture aerodynamics and combustion. The present inventors havesurprisingly found that a lean burn combustor according to thedisclosure can be scaled up and down without affecting the combustionefficiency. In other words, as the ratio D/d is non-dimensional, for awide size range of the combustor chamber of the lean burn combustoraccording to the disclosure, the S-shaped recirculation zone can beeffectively and efficiently formed within the primary combustion zone.

For example, a lean burn combustor according to the disclosure may besized for engines adapted to be mounted on small, medium, and largeaircrafts.

In embodiments, the ratio D/d of the primary combustion zone depth tothe lean burn fuel injector head tip diameter may be less than 2.3, forexample less than 2.2, or less than 2.1, or less than 2.0.

The ratio D/d of the primary combustion zone depth D to the lean burnfuel injector head tip diameter d may be greater than 1.2. Inembodiments, the ratio D/d of the primary combustion zone depth D to thelean burn fuel injector head tip diameter d may be greater than 1.3, forexample greater than 1.4, or greater than 1.5.

The lean burn fuel injector head may generally extend along alongitudinal direction, the longitudinal direction forming a cant anglewith the axial direction, the cant angle being comprised between 0° and10°.

The combustor chamber may extend axially between the meter panel(upstream) and an annular outlet (downstream), through which thecombusted gas exits the combustor chamber. The annular outlet may bedefined by, and between, the radially inner annular wall and theradially outer annular wall of the combustor chamber. In the presentdisclosure the combustor chamber length (L) may be defined as an axialdistance between the meter panel and the annular outlet.

The radially outer annular wall may extend substantially axially betweenthe meter panel and the annular outlet. In embodiments, the radiallyouter annular wall may form an outer angle α_(outer) with the axialdirection, the outer angle α_(outer) being comprised between 0° and 15°,for example between 0° and 12°, or between 0° and 10°, or between 3° and15°, or between 5° and 15°.

The radially outer annular wall may comprise a first part and a secondpart. The first part of the radially outer annular wall may be arrangedupstream of the second part of the radially outer annular wall. Thefirst part and the second part of the radially outer annular wall may bemutually aligned.

The radially inner annular wall may comprise a first part and a secondpart. The first part of the radially inner annular wall may be arrangedupstream of the second part of the radially inner annular wall. Thefirst part of the radially inner annular wall may be connected to themeter panel. The second part of the radially inner annular wall and thesecond part of the radially outer annular wall may define the annularoutlet of the combustion chamber. The first part of the radially innerannular wall may be arranged at an angle to the second part of theradially inner annular wall. The first part of the radially innerannular wall may be parallel to the radially outer annular wall. Thefirst part of the radially inner annular wall may be parallel to theaxial direction.

The first part of the radially inner annular wall, the first part of theradially outer annular wall, and the meter panel define the primarycombustion zone.

In the present disclosure the primary combustion zone length (Z) may bedefined as axial length of the primary combustion zone. The first partof the radially inner annular wall may define the primary combustionzone length (Z). The first part of the radially outer annular wall maydefine the primary combustion zone length (Z). The first part of theradially inner annular wall and the first part of the radially outerannular wall may have the same length along the axial direction.

In the present disclosure the primary combustion zone depth (D) may bedefined as radial distance between the first part of the radially innerannular wall and the first part of the radially outer annular wall. Theterm “radial” as used herein may refer to the direction perpendicular tothe first part of the radially inner annular wall and the first part ofthe radially outer annular wall.

The second part of the radially inner annular wall may be convergenttowards the second part of the radially outer annular wall in adownstream direction. In embodiments, the second part of the radiallyinner annular wall may form an inner angle α_(inner) with the first partof the radially inner annular wall, the inner angle α_(inner) beingcomprised between 15° and 50°, for example between 15° and 45°, orbetween 15° and 40°, or between 20° and 50°, or between 25° and 50°, orbetween 25° and 45°, or between 25° and 40°.

The second part of the radially inner annular wall and the second partof the radially outer annular wall may define the secondary combustionzone. The secondary combustion zone may extend between the primarycombustion zone and the annular outlet of the combustion chamber. Thesecondary combustion zone is arranged downstream of the primarycombustion zone. The secondary combustion zone extends for the secondarycombustion zone length (L-Z). The second part of the radially outerannular wall may extend for a length equal to the secondary combustionzone length (L-Z). The second part of the radially inner annular wallmay extend for a length equal to (L-Z)/cos(α_(inner)).

Respective inner surfaces of the radially inner annular wall, radiallyouter annular wall, and meter panel may define the size and shape of thecombustion chamber where combustion occurs. In some literature, theradially inner annular wall, radially outer annular wall, and meterpanel are referred to as combustion liners. In embodiments, the radiallyinner annular wall, radially outer annular wall, and meter panel mayeach comprise respective tiles. The tiles may define the respectiveinner surfaces of the radially inner annular wall, radially outerannular wall, and meter panel, and therefore define the size and shapeof the combustor chamber where combustion occurs. The tiles, or in otherwords the inner surfaces of the radially inner annular wall, radiallyouter annular wall, and meter panel may face the combustion processwithin the combustion chamber and may be in contact with the fuel andair mixture, and/or the combustion gases.

The inventors of the present disclosure have also found that othernon-dimensional parameters may be advantageous when designing acombustor chamber for a lean burn combustor with improved combustionefficiency.

In embodiments, a ratio Z/d of the primary combustion zone length Z tothe lean burn fuel injector head tip diameter d may be less than 1.40,for example less than 1.35, or less than 1.30, or less than 1.25, orless than 1.20. The ratio Z/d of the primary combustion zone length Z tothe lean burn fuel injector head tip diameter d may be greater than0.70, for example greater than 0.75, or greater than 0.80, or greaterthan 0.85, or greater than 0.90.

In embodiments, a ratio L/D of the combustor chamber length L to theprimary combustion zone depth D may be less than 2.0, for example lessthan 1.9, or less than 1.8, or less than 1.75, or less than 1.70, orless than 1.65, or less than 1.60. The ratio L/D of the combustorchamber length L to the primary combustion zone depth D may be greaterthan 1.0, for example greater than 1.05, or greater than 1.10, orgreater than 1.15, or greater than 1.20, or greater than 1.25.

In embodiments, a ratio L/d of the combustor chamber length L to thelean burn fuel injector head tip diameter d may be less than 5, forexample less than 4.5, or less than 4, or less than 3.5, or less than 3,or less than 2.8, or less than 2.6, or less than 2.5, or less than 2.45,or less than 2.4. The ratio L/d of the combustor chamber length L to thelean burn fuel injector head tip diameter d may be greater than 1.5, forexample greater than 1.7, or greater than 1.8, or greater than 1.85, orgreater than 1.9, or greater than 2.0.

The skilled person would appreciate that, as the ratios Z/d of theprimary combustion zone length Z to the lean burn fuel injector head tipdiameter d, L/D of the combustor chamber length L to the primarycombustion zone depth D, and L/d of the combustor chamber length L tothe lean burn fuel injector head tip diameter d are all non-dimensional,they all may apply to lean burn combustors, and relative combustorchambers, of a wide size range and may contribute to form the S-shapedrecirculation zone within the primary combustion zone.

According to a second aspect, there is provided a lean burn combustorcomprising: a plurality of lean burn fuel injectors, each comprising afuel feed arm and a lean burn fuel injector head with a lean burn fuelinjector head tip, wherein the lean burn fuel injector head tip has alean burn fuel injector head tip diameter (d), the lean burn fuelinjector head comprising a pilot fuel injector and a main fuel injector,the main fuel injector being arranged coaxially and radially outwards ofthe pilot fuel injector; and a combustor chamber extending along anaxial direction and comprising a radially inner annular wall, a radiallyouter annular wall, and a meter panel provided upstream of the radiallyinner and radially outer annular walls with a plurality of aperturesadapted for accommodating the lean burn fuel injector head tips. Theradially inner annular wall, the radially outer annular wall, and themeter panel define the size and shape of the combustor chamber, whereinthe combustor chamber has a combustor chamber length (L) and comprises aprimary combustion zone with a primary combustion zone length (Z) and aprimary combustion zone depth (D), and a secondary combustion zone witha secondary combustion zone length (L-Z) arranged downstream of theprimary combustion zone. According to the second aspect, a ratio L/D ofthe combustor chamber length to the primary combustion zone depth isless than 1.8.

In embodiments, a ratio L/D of the combustor chamber length L to theprimary combustion zone depth D may be less than 1.75, for example lessthan 1.70, or less than 1.65, or less than 1.60. The ratio L/D of thecombustor chamber length L to the primary combustion zone depth D may begreater than 1.0, for example greater than 1.05, or greater than 1.10,or greater than 1.15, or greater than 1.20, or greater than 1.25.

In embodiments, a ratio L/d of the combustor chamber length L to thelean burn fuel injector head tip diameter d may be less than 5, forexample less than 4.5, or less than 4, or less than 3.5, or less than 3,or less than 2.8, or less than 2.6, or less than 2.5, or less than 2.45,or less than 2.4. The ratio L/d of the combustor chamber length L to thelean burn fuel injector head tip diameter d may be greater than 1.8, forexample greater than 1.85, or greater than 1.9, or greater than 2.0.

In embodiments, a ratio D/d of the primary zone depth D to the lean burnfuel injector head tip diameter d may be less than 2.4, for example lessthan 2.3, or less than 2.2, or less than 2.1, or less than 2.0. Theratio D/d of the primary combustion zone depth D to the lean burn fuelinjector head tip diameter d may be greater than 1.2, for examplegreater than 1.3, or greater than 1.4, or greater than 1.5.

In embodiments, a ratio Z/d of the primary combustion zone length Z tothe lean burn fuel injector head tip diameter d may be less than 1.40,for example less than 1.35, or less than 1.30, or less than 1.25, orless than 1.20. The ratio Z/d of the primary combustion zone length Z tothe lean burn fuel injector head tip diameter d may be greater than0.70, for example greater than 0.75, or greater than 0.80, or greaterthan 0.85, or greater than 0.90.

According to a third aspect, there is provided a lean burn combustorcomprising: a plurality of lean burn fuel injectors, each comprising afuel feed arm and a lean burn fuel injector head with a lean burn fuelinjector head tip, wherein the lean burn fuel injector head tip has alean burn fuel injector head tip diameter (d), the lean burn fuelinjector head comprising a pilot fuel injector and a main fuel injector,the main fuel injector being arranged coaxially and radially outwards ofthe pilot fuel injector; and a combustor chamber extending along anaxial direction and comprising a radially inner annular wall, a radiallyouter annular wall, and a meter panel provided upstream of the radiallyinner and radially outer annular walls with a plurality of aperturesadapted for accommodating the lean burn fuel injector head tips. Theradially inner annular wall, the radially outer annular wall, and themeter panel define the size and shape of the combustor chamber, whereinthe combustor chamber has a combustor chamber length (L) and comprises aprimary combustion zone with a primary combustion zone length (Z) and aprimary combustion zone depth (D), and a secondary combustion zone witha secondary combustion zone length (L-Z) arranged downstream of theprimary combustion zone. According to the third aspect, a ratio L/d ofthe combustor chamber length to the lean burn fuel injector head tipdiameter is less than 5.

In embodiments the ratio L/d of the combustor chamber length L to thelean burn fuel injector head tip diameter d may be less than 4.5, forexample less than 4, or less than 3.5, or less than 3, or less than 2.8,or less than 2.6, or less than 2.5, or less than 2.45, or less than 2.4.The ratio L/d of the combustor chamber length L to the lean burn fuelinjector head tip diameter d may be greater than 1.5, for examplegreater than 1.7, or greater than 1.8, or greater than 1.85, or greaterthan 1.9, or greater than 2.0.

In embodiments, a ratio D/d of the primary zone depth D to the lean burnfuel injector head tip diameter d may be less than 2.4, for example lessthan 2.3, or less than 2.2, or less than 2.1, or less than 2.0. Theratio D/d of the primary combustion zone depth D to the lean burn fuelinjector head tip diameter d may be greater than 1.2, for examplegreater than 1.3, or greater than 1.4, or greater than 1.5.

In embodiments, a ratio L/D of the combustor chamber length L to theprimary combustion zone depth D may be less than 2.0, for example lessthan 1.9, or less than 1.8, or less than 1.75, or less than 1.70, orless than 1.65, or less than 1.60. The ratio L/D of the combustorchamber length L to the primary combustion zone depth D may be greaterthan 1.0, for example greater than 1.05, or greater than 1.10, orgreater than 1.15, or greater than 1.20, or greater than 1.25.

In embodiments, a ratio Z/d of the primary combustion zone length Z tothe lean burn fuel injector head tip diameter d may be less than 1.40,for example less than 1.35, or less than 1.30, or less than 1.25, orless than 1.20. The ratio Z/d of the primary combustion zone length Z tothe lean burn fuel injector head tip diameter d may be greater than0.70, for example greater than 0.75, or greater than 0.80, or greaterthan 0.85, or greater than 0.90.

In embodiments, the lean burn combustor of the first, second, and thirdaspect described above may comprise a pre-diffuser, arranged upstream ofthe lean burn fuel injector head and adapted for providing the combustorchamber with compressed air. In some literature, the pre-diffuser issimply referred to as diffuser. The pre-diffuser may be generallyannular and may include radially inner and radially outer walls definingan outlet for the compressed air. In the present disclosure a damp gap(g) may be defined as axial distance between a mid-point between theradially inner and radially outer walls of the pre-diffuser at saidoutlet and a mid-point between the radially inner and radially outerannular walls of the combustor chamber at the meter panel. A ratio g/dof the damp gap g to the lean burn fuel injector head tip diameter d maybe less than 1.30, for example less than 1.25, or less than 1.2, or lessthan 1.15. The ratio g/d of the damp gap g to the lean burn fuelinjector head tip diameter d may be greater than 0.65, for examplegreater than 0.7, or greater than 0.75, or greater than 0.8, or greaterthan 0.85.

The skilled person would appreciate that also the ratio g/d of the dampgap g to the lean burn fuel injector head tip diameter d isnon-dimensional and may apply to lean burn combustors, and relativecombustor chambers, of a wide size range and may contribute to form theS-shaped recirculation zone within the primary combustion zone.

According to a forth aspect, there is provided a lean burn combustorcomprising: a plurality of lean burn fuel injectors, each comprising afuel feed arm and a lean burn fuel injector head with a lean burn fuelinjector head tip, wherein the lean burn fuel injector head tip has alean burn fuel injector head tip diameter (d), the lean burn fuelinjector head comprising a pilot fuel injector and a main fuel injector,the main fuel injector being arranged coaxially and radially outwards ofthe pilot fuel injector; and a combustor chamber extending along anaxial direction and comprising a radially inner annular wall, a radiallyouter annular wall, and a meter panel provided upstream of the radiallyinner and radially outer annular walls with a plurality of aperturesadapted for accommodating the lean burn fuel injector head tips. Theradially inner annular wall, the radially outer annular wall, and themeter panel define the size and shape of the combustor chamber. The leanburn combustor of the forth aspect further includes a pre-diffuser,arranged upstream of the lean burn fuel injector head and adapted forproviding the combustor chamber with compressed air. The pre-diffuser isgenerally annular and includes radially inner and radially outer wallsdefining an outlet for the compressed air. A damp gap (g) is defined asaxial distance between a mid-point between the radially inner andradially outer walls of the pre-diffuser at said outlet and a mid-pointbetween the radially inner and radially outer annular walls of thecombustor chamber at the meter panel, wherein a ratio g/d of the dampgap to the lean burn fuel injector head tip diameter is less than 1.30.

In embodiments, the ratio g/d of the damp gap g to the lean burn fuelinjector head tip diameter d may be less than 1.25, for example lessthan 1.2, or less than 1.15. The ratio g/d of the damp gap g to the leanburn fuel injector head tip diameter d may be greater than 0.65, forexample greater than 0.7, or greater than 0.75, or greater than 0.8, orgreater than 0.85.

The combustor chamber of the lean burn combustor of the forth aspect hasa combustor chamber length (L) and may define a primary combustion zonewith a primary combustion zone length (Z) and a primary combustion zonedepth (D), and a secondary combustion zone with a secondary combustionzone length (L-Z) arranged downstream of the primary combustion zone.

In embodiments, a ratio D/d of the primary zone depth D to the lean burnfuel injector head tip diameter d may be less than 2.4, for example lessthan 2.3, or less than 2.2, or less than 2.1, or less than 2.0. Theratio D/d of the primary combustion zone depth D to the lean burn fuelinjector head tip diameter d may be greater than 1.2, for examplegreater than 1.3, or greater than 1.4, or greater than 1.5.

In embodiments, a ratio L/D of the combustor chamber length L to theprimary combustion zone depth D may be less than 2.0, for example lessthan 1.9, or less than 1.8, or less than 1.75, or less than 1.70, orless than 1.65, or less than 1.60. The ratio L/D of the combustorchamber length L to the primary combustion zone depth D may be greaterthan 1.0, for example greater than 1.05, or greater than 1.10, orgreater than 1.15, or greater than 1.20, or greater than 1.25.

In embodiments, a ratio L/d of the combustor chamber length L to thelean burn fuel injector head tip diameter d may be less than 5, forexample less than 4.5, or less than 4, or less than 3.5, or less than 3,or less than 2.8, or less than 2.6, or less than 2.5, or less than 2.45,or less than 2.4. The ratio L/d of the combustor chamber length L to thelean burn fuel injector head tip diameter d may be greater than 1.5, forexample greater than 1.7, or greater than 1.8, or greater than 1.85, orgreater than 1.9, or greater than 2.0.

In embodiments, a ratio Z/d of the primary combustion zone length Z tothe lean burn fuel injector head tip diameter d may be less than 1.40,for example less than 1.35, or less than 1.30, or less than 1.25, orless than 1.20. The ratio Z/d of the primary combustion zone length Z tothe lean burn fuel injector head tip diameter d may be greater than0.70, for example greater than 0.75, or greater than 0.80, or greaterthan 0.85, or greater than 0.90.

According to a fifth aspect, there is provided a gas turbine enginecomprising a lean burn combustor according to any one of the aspectsdescribed above.

The gas turbine engine of the fifth aspect may be a gas turbine enginefor an aircraft, or for industrial and marine applications.

In embodiments, the gas turbine engine may further comprise: an enginecore comprising a compressor, a combustor, a turbine, and a core shaftconnecting the turbine to the compressor; and a fan located upstream ofthe engine core, the fan comprising a plurality of fan blades, whereinthe combustor is the lean burn combustor according to any one of thefirst, second, third, and forth aspect.

In embodiments, the compressor and turbine may rotate about an engineprincipal rotational axis, and the axial direction of the combustorchamber may be parallel to the engine principal rotational axis.

In embodiment, the turbine may be a first turbine, the compressor may bea first compressor, and the core shaft may be a first core shaft. Theengine core may further comprise a second turbine, a second compressor,and a second core shaft connecting the second turbine to the secondcompressor. The second turbine, second compressor, and second core shaftmay be arranged to rotate at a higher rotational speed than the firstcore shaft.

As previously noted, the lean burn combustor according to the disclosuremay be sized for engines adapted to be mounted on small, medium, andlarge aircrafts. Accordingly, the fan of the gas turbine engineaccording to the fifth aspect may have a fan diameter greater than (oron the order of) any of: 220 cm, 230 cm, 240 cm, 250 cm (around 100inches), 260 cm, 270 cm (around 105 inches), 280 cm (around 110 inches),290 cm (around 115 inches), 300 cm (around 120 inches), 310 cm, 320 cm(around 125 inches), 330 cm (around 130 inches), 340 cm (around 135inches), 350 cm, 360 cm (around 140 inches), 370 cm (around 145 inches),380 (around 150 inches) cm, 390 cm (around 155 inches), 400 cm, 410 cm(around 160 inches) or 420 cm (around 165 inches). The fan diameter maybe in an inclusive range bounded by any two of the values in theprevious sentence (i.e. the values may form upper or lower bounds), forexample in the range of from 220 cm to 420 cm, or 240 cm to 380 cm, or240 cm to 280 cm, or 330 cm to 380 cm.

Arrangements of the present disclosure may be particularly, although notexclusively, beneficial for fans that are driven via a gearbox.Accordingly, the gas turbine engine may comprise a gearbox that receivesan input from the core shaft and outputs drive to the fan so as to drivethe fan at a lower rotational speed than the core shaft. The input tothe gearbox may be directly from the core shaft, or indirectly from thecore shaft, for example via a spur shaft and/or gear. The core shaft mayrigidly connect the turbine and the compressor, such that the turbineand compressor rotate at the same speed (with the fan rotating at alower speed).

The gas turbine engine as described and/or claimed herein may have anysuitable general architecture. For example, the gas turbine engine mayhave any desired number of shafts that connect turbines and compressors,for example one, two or three shafts. Purely by way of example, theturbine connected to the core shaft may be a first turbine, thecompressor connected to the core shaft may be a first compressor, andthe core shaft may be a first core shaft. The engine core may furthercomprise a second turbine, a second compressor, and a second core shaftconnecting the second turbine to the second compressor. The secondturbine, second compressor, and second core shaft may be arranged torotate at a higher rotational speed than the first core shaft.

In such an arrangement, the second compressor may be positioned axiallydownstream of the first compressor. The second compressor may bearranged to receive (for example directly receive, for example via agenerally annular duct) flow from the first compressor.

The gearbox may be arranged to be driven by the core shaft that isconfigured to rotate (for example in use) at the lowest rotational speed(for example the first core shaft in the example above). For example,the gearbox may be arranged to be driven only by the core shaft that isconfigured to rotate (for example in use) at the lowest rotational speed(for example only be the first core shaft, and not the second coreshaft, in the example above). Alternatively, the gearbox may be arrangedto be driven by any one or more shafts, for example the first and/orsecond shafts in the example above.

The gearbox may be a reduction gearbox (in that the output to the fan isa lower rotational rate than the input from the core shaft). Any type ofgearbox may be used. For example, the gearbox may be a “planetary” or“star” gearbox, as described in more detail elsewhere herein. Thegearbox may have any desired reduction ratio (defined as the rotationalspeed of the input shaft divided by the rotational speed of the outputshaft), for example greater than 2.5, for example in the range of from 3to 4.2, or 3.2 to 3.8, for example on the order of or at least 3, 3.1,3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1 or 4.2. The gear ratiomay be, for example, between any two of the values in the previoussentence. Purely by way of example, the gearbox may be a “star” gearboxhaving a ratio in the range of from 3.1 or 3.2 to 3.8.

According to an aspect, there is provided an aircraft comprising a gasturbine engine as described and/or claimed herein. The aircraftaccording to this aspect is the aircraft for which the gas turbineengine has been designed to be attached.

The skilled person will appreciate that except where mutually exclusive,a feature or parameter described in relation to any one of the aboveaspects may be applied to any other aspect. Furthermore, except wheremutually exclusive, any feature or parameter described herein may beapplied to any aspect and/or combined with any other feature orparameter described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described by way of example only, with referenceto the Figures, in which:

FIG. 1 is a sectional side view of a gas turbine engine;

FIG. 2 is a close up sectional side view of an upstream portion of thegas turbine engine of FIG. 1;

FIG. 3 is a partially cut-away view of a gearbox for a gas turbineengine;

FIG. 4 is a partial rear view of a lean burn combustor according to thedisclosure;

FIG. 5 is a sectional side view of the lean burn combustor of FIG. 4along arrows A-A; and

FIG. 6 is a schematic representation of an S-shaped flow recirculationin a primary combustion zone of the lean burn combustor of FIGS. 4 and5.

DETAILED DESCRIPTION OF THE DISCLOSURE

With reference to FIG. 1, a gas turbine engine, generally indicated at10, has an engine principal rotational axis 9. The engine 10 comprisesan air intake 12 and a propulsive fan with a plurality of fan blades 23that generates two airflows: a core airflow A and a bypass airflow B.The gas turbine engine 10 comprises a core 11 that receives the coreairflow A. The engine core 11 comprises, in axial flow series, a lowpressure compressor 14, a high-pressure compressor 15, combustionequipment comprising a lean burn combustor 16, a high-pressure turbine17, a low pressure turbine 19 and a core exhaust nozzle 20. A nacelle 21generally surrounds the gas turbine engine 10 and defines a bypass duct22 and a bypass exhaust nozzle 18. The bypass airflow B flows throughthe bypass duct 22. The fan is attached to and driven by the lowpressure turbine 19 via a shaft 26 and an epicyclic gearbox 30.

In use, the core airflow A is accelerated and compressed by the lowpressure compressor 14 and directed into the high pressure compressor 15where further compression takes place. The compressed air exhausted fromthe high pressure compressor 15 is directed into the combustionequipment 16 where it is mixed with fuel and the mixture is combusted.The resultant hot combustion products then expand through, and therebydrive, the high pressure and low pressure turbines 17, 19 before beingexhausted through the nozzle 20 to provide some propulsive thrust. Thehigh pressure turbine 17 drives the high pressure compressor 15 by asuitable interconnecting shaft 27. The fan generally provides themajority of the propulsive thrust. The epicyclic gearbox 30 is areduction gearbox.

Note that the terms “low pressure turbine” and “low pressure compressor”as used herein may be taken to mean the lowest pressure turbine stagesand lowest pressure compressor stages (i.e. not including the fan)respectively and/or the turbine and compressor stages that are connectedtogether by the interconnecting shaft 26 with the lowest rotationalspeed in the engine (i.e. not including the gearbox output shaft thatdrives the fan). In some literature, the “low pressure turbine” and “lowpressure compressor” referred to herein may alternatively be known asthe “intermediate pressure turbine” and “intermediate pressurecompressor”. Where such alternative nomenclature is used, the fan may bereferred to as a first, or lowest pressure, compression stage.

Other gas turbine engines to which the present disclosure may be appliedmay have alternative configurations. By way of example, such engines mayhave an alternative number of interconnecting shafts (e.g. two) and/oran alternative number of compressors and/or turbines. Further, theengine may be an ungeared engine, i.e. the engine may not comprise agearbox provided in the drive train from the turbine to the compressorand/or fan.

FIG. 2 illustrates in greater detail the gearbox 30 of the gas turbineengine 10. The low pressure turbine 19 (see FIG. 1) drives the shaft 26,which is coupled to a sun wheel, or sun gear, 28 of the epicyclic geararrangement 30. Radially outwardly of the sun gear 28 and intermeshingtherewith is a plurality of planet gears 32 that are coupled together bya planet carrier 34. The planet carrier 34 constrains the planet gears32 to process around the sun gear 28 in synchronicity whilst enablingeach planet gear 32 to rotate about its own axis. The planet carrier 34is coupled via linkages 36 to the fan 23 in order to drive its rotationabout the engine axis 9. Radially outwardly of the planet gears 32 andintermeshing therewith is an annulus or ring gear 38 that is coupled,via linkages 40, to a stationary supporting structure 24.

The epicyclic gearbox 30 is shown by way of example in greater detail inFIG. 3. Each of the sun gear 28, planet gears 32 and ring gear 38comprise teeth about their periphery to intermesh with the other gears.However, for clarity only exemplary portions of the teeth areillustrated in FIG. 3. There are four planet gears 32 illustrated,although it will be apparent to the skilled reader that more or fewerplanet gears 32 may be provided within the scope of the claimedinvention. Practical applications of a planetary epicyclic gearbox 30generally comprise at least three planet gears 32.

The epicyclic gearbox 30 illustrated by way of example in FIGS. 2 and 3is of the planetary type, in that the planet carrier 34 is coupled to anoutput shaft via linkages 36, with the ring gear 38 fixed. However, anyother suitable type of epicyclic gearbox 30 may be used. By way offurther example, the epicyclic gearbox 30 may be a star arrangement, inwhich the planet carrier 34 is held fixed, with the ring (or annulus)gear 38 allowed to rotate. In such an arrangement the fan 23 is drivenby the ring gear 38. By way of further alternative example, the gearbox30 may be a differential gearbox in which the ring gear 38 and theplanet carrier 34 are both allowed to rotate.

It will be appreciated that the arrangement shown in FIGS. 2 and 3 is byway of example only, and various alternatives are within the scope ofthe present disclosure. Accordingly, the present disclosure extends to agas turbine engine having any arrangement of gearbox styles (for examplestar or planetary), support structures, input and output shaftarrangement, and bearing locations.

FIGS. 4 and 5 illustrate the lean burn combustor 16 in greater detail.

The lean burn combustor 16 comprises a plurality of lean burn fuelinjectors 50, each comprising a fuel feed arm 52 and a lean burn fuelinjector head 54. The fuel feed arm 52 delivers fuel from a distributionsystem (not illustrated) to the lean burn fuel injector head 54, wherefuel and air are mixed.

The lean burn fuel injector head 54 comprises a pilot fuel injector 56and a radially outer main fuel injector 58. The main fuel injector 58 isarranged coaxially around the pilot fuel injector 56. The lean burn fuelinjector head 54 further comprises air swirlers (not illustrated forsake of simplicity). According to known arrangements, the lean burn fuelinjector head 54 may comprise three, four, or five air swirlers adaptedto provide swirling air flows which atomise the fuel from the pilot andmain fuel injectors. The air swirlers may comprise swirling vanes.

For example, in a three air swirler arrangement, the pilot fuel injectoris provided between inner and outer air swirlers, the main fuel injectoris also provided between inner and out air swirlers, the pilot fuelinjector outer air swirler being the main fuel injector inner airswirler. In a four swirler arrangement, the pilot fuel injector and themain fuel injector do not share air swirlers, such that each of thepilot fuel injector and main fuel injector comprises its own set ofinner and outer air swirler. In a five swirler arrangement, anadditional air swirler is provided between the outer air swirler of thepilot fuel injector and the inner air swirler of the main fuel injector.

The lean burn combustor 16 further comprises a combustor chamber 60extending along an axial direction 62. In the illustrated embodiment,the axial direction 62 is substantially parallel to the engine principalrotational axis 9. In other non-illustrated embodiments, the axialdirection 62 may not be parallel to the engine principal rotational axis9. In other words, the combustion chambers may extend at an angle to theaxial direction 62, for example at an angle comprised between 0° and20°.

The combustor chamber 60 comprises a radially inner annular wall 64, aradially outer annular wall 66, and a meter panel 68 provided upstreamof the radially inner and radially outer annular walls 64, 66. Axiallyopposite to the meter panel 68, the combustor chamber 60 features anannular outlet 67, through which the combusted gas exits the combustorchamber 60. The annular outlet is defined between respective downstreamend portions of the radially inner annular wall 64 and the radiallyouter annular wall 66 of the combustor chamber 60. In other words, thecombustor chamber 60 extends axially from the upstream meter plate 68and the downstream annular outlet 67 for a length L.

The meter panel 68 is provided with a plurality of apertures 70 foraccommodating the lean burn fuel injectors 50. In detail, the lean burnfuel injectors 50 are connected to the meter panel 68 at a tip 72 of thelean burn fuel injector head 54 that is coaxially housed in the aperture70.

The lean burn fuel injector head 54 may generally extend along alongitudinal direction 55. In the illustrated embodiment, thelongitudinal direction 55 is parallel to the axial direction 62. Inother words, a cant angle defined between the longitudinal 55 and theaxial direction 62 is 0°. In non-illustrated embodiment, the lean burnfuel injector head 54 may not be coaxial with the aperture 70, or inother words the cant angle may be different from 0°, for examplecomprised between 0° and 10°.

The lean burn fuel injectors 50 are configured to inject fuel and airinto the combustor chamber 50. A meter panel mid-point 69 is defined atthe meter panel 68 mid-way between the radially inner annular wall 64and the radially outer annular wall 66.

The lean burn fuel injector head tip 72 features a lean burn fuelinjector head tip diameter d, which corresponds to the diameter of theaperture 70.

The radially inner annular wall 64 and the radially outer annular wall66 are connected to the meter panel 68 at their upstream end portions.The radially inner annular wall 64, radially outer annular wall 66, andmeter panel 68 define with respective inner surfaces the size and shapeof the combustor chamber 60.

In embodiments not illustrated, the radially inner annular wall 64,radially outer annular wall 66, and meter panel 68 may each compriserespective tiles. If present, the tiles define the respective innersurfaces of the radially inner annular wall 64, radially outer annularwall 66, and meter panel 68, and therefore the size and shape of thecombustor chamber 60 where combustion occurs. The tiles, or in otherwords the inner surfaces of the radially inner annular wall 64, radiallyouter annular wall 66, and meter panel 68 face the combustion processwithin the combustion chamber 60 and are in contact with the fuel andair mixture and/or combustion gasses.

The radially outer annular wall 66 extends substantially axially betweenthe meter panel 68 and the annular outlet 67. In other words, theradially outer annular wall 66 forms an outer angle α_(outer) with theaxial direction 62 substantially equal to 0°. In non-illustratedembodiments, the radially outer annular wall 66 may extend along adirection which forms with the axial direction 62 an outer angleα_(outer) different from 0°, for example comprised between 0° and 15°.

The radially outer annular wall 66 comprises a first part 74 and asecond part 75. The first part 74 of the radially outer annular wall 66is arranged upstream of the second part 75 of the radially outer annularwall 66. An upstream portion of the first part 74 of the radially outerannular wall 66 is connected to the meter panel 68. A downstream endportion of the second part 75 of the radially outer annular wall 66define the annular outlet 67 of the combustion chamber 60. In theillustrated embodiment, the first part 74 and the second part 75 of theradially outer annular wall 66 are integral and mutually aligned alongthe axial direction 62.

The radially inner annular wall 64 comprise a first part 76 and a secondpart 77. The first part 76 of the radially inner annular wall 64 isarranged upstream of the second part 77 of the radially inner annularwall 64. An upstream portion of the first part 76 of the radially innerannular wall 64 is connected to the meter panel 68. A downstream endportion of the second part 77 of the radially inner annular wall 64along with the downstream end portion of the second part 75 of theradially outer annular wall 66 define the annular outlet 67 of thecombustion chamber 60. The first part 76 of the radially inner annularwall 64 is arranged at an angle to the second part 77 of the radiallyinner annular wall 64. The first part 76 of the radially inner annularwall 64 is generally parallel to the axial direction 62. The first part76 of the radially inner annular wall 64 is generally parallel to thefirst part 74 of the radially outer annular wall 66. The second part 75of the radially inner annular wall 64 is convergent towards the radiallyouter annular wall 66 in a downstream direction to form the annularoutlet 67. The second part 77 of the radially inner annular wall 64 isarranged at an angle to the first part 76 of the radially inner annularwall 64. Moreover, the second part 77 of the radially inner annular wall64 forms an inner angle α_(inner) with the first part 76 of the radiallyinner annular wall 64. The inner angle α_(inner) is generally comprisedbetween 25° and 40°. As the first part 76 of the radially inner annularwall 76 and the radially outer annular wall 74 are generally parallel tothe axial direction 62, the second part 77 of the radially inner annularwall 64 is arranged at the inner angle α_(inner) to the axial direction62 and to the radially outer annular wall 74.

The combustor chamber 60 comprises a primary combustion zone 80 and asecondary combustion zone 82.

The primary combustion zone 80 is defined by the first part 76 of theradially inner annular wall 64, the first part 74 of the radially outerannular wall 66, and the meter panel 68. The primary combustion zone 80is annular in cross-section and extends axially from the meter panel 68for a length Z. In the embodiment illustrated, both the first part 74 ofthe radially outer annular wall 66 and the first part 76 of the radiallyinner annular wall 64 extend axially for the length Z. Moreover, theprimary combustion zone 80 extends radially, i.e. in a directionperpendicular to the axial direction 62, for a depth D between the firstpart 76 of the radially inner annular wall 64 and the first part 74 ofthe radially outer annular wall 66.

The secondary combustion zone 82, which is arranged downstream of theprimary combustion zone 80, is defined by the second part 77 of theradially inner annular wall 64 and the second part 75 of the radiallyouter annular wall 66. In practice, the secondary combustion zone 82extends from a downstream end portion of the primary combustion zone 80to the annular outlet 67. The secondary combustion zone 82 extendsaxially for a length L-Z. In the embodiment described, the second part75 of the radially outer annular wall 66 extends for the same length L-Zand the second part 77 of the radially inner annular wall 64 extends fora length equal to (L-Z)·sin α_(inner). The second combustion zone 82 isannular- and frusto-conical-shaped and convergent downstream towards theannular outlet 67.

The combustion chamber 60 is dimensioned such that the ratio D/d of theprimary combustion zone depth D to the lean burn fuel injector head tipdiameter d is comprised between 1.2 and 2.4, preferably between 2.0 and2.4. In an embodiment, the combustor chamber 60 has a ratio D/d of 2.2.The ratio D/d being comprised between 1.2 and 2.4, preferably between2.0 and 2.4, allows to optimise the aerodynamics of the fuel and airmixture coming from the main and pilot fuel injectors 56, 58 andrelative air swirler, and increase combustion efficiency.

This will be described in greater detail with reference to FIG. 6.

The pilot fuel and air mixture travels along a so-called S-shapedtrajectory 86 within the primary combustion zone 80. The pilot fuel andair mixture coming from the lean burn fuel injector head tip 72 arrivesat a stagnation point SP where the pilot fuel and air mixture localvelocity is zero, and is then diverted backwards towards the radiallyouter and radially inner annular wall 74, 76 (due to low static pressureexerted by the main fuel and air mixture 84) where the pilot fuel andair mixture enters in contact and supports/stabilises the combustion ofthe main fuel and air mixture 84.

The ratio D/d being comprised between 1.2 and 2.4, preferably between2.0 and 2.4, allows to achieve the S-shaped flow recirculation of thepilot fuel and air mixture within the primary combustion zone 80. Inother words, the pilot fuel and air mixture stagnation point SP iswithin the primary combustion zone 80 and the pilot fuel and air mixturemixes with the fuel main and air mixture 84 within the primarycombustion zone 80.

Other non-dimensional parameter may have a positive effect on theformation of the pilot fuel and air mixture S-shaped trajectory 86within the primary combustion zone 80.

The combustion chamber 60 may be dimensioned such that a ratio Z/d ofthe primary combustion zone length L to the lean burn fuel injector headtip diameter d is greater than 0.70 and less than 1.40, preferablycomprised between 0.9 and 1.25. In an embodiment, the combustor chamber60 may have a ratio Z/d of 1.05.

Moreover, the combustion chamber 60 may be dimensioned such that a ratioL/D of the combustor chamber length L to the primary combustion zonedepth D is less than 2.0, for example less 1.60, and greater than 1.0,for example greater than 1.25. In an embodiment, the combustor chamber60 may have a ratio L/D of 1.5.

Furthermore, the combustor chamber 60 may dimensioned such that a ratioL/d of the combustor chamber length L to the lean burn fuel injectorhead tip diameter d is less than 5, or less than 2.5, and greater than1.5, or greater than 2.0. In an embodiment, the combustor chamber 60 mayhave a ratio L/d of 3.5.

The above ratios (Z/d, L/D, and L/d) may contribute to optimise theaerodynamics of the fuel and air mixture coming from the main and pilotfuel injectors 56, 58 and relative air swirler, and increase combustionefficiency.

It should be noted that all of the above ratios (D/d, Z/d, L/D, and L/d)are non-dimensional and therefore apply to lean burn combustors of awide size range. For example, D may be comprised between 90 mm and 150mm, for example between 110 mm and 140 mm, d may be comprised between 60mm and 100 mm, for example between 70 mm and 85 mm, Z may be comprisedbetween 50 mm and 130 mm, for example between 60 mm and 110 mm, and Lmay be comprised between 100 mm and 200 mm.

The lean burn combustor 16 further comprises a pre-diffuser 90 forproviding the lean burn fuel injector head 54 with compressed air fromthe high-pressure compressor 15. The pre-diffuser is annular andincludes a radially inner wall 92 and a radially outer wall 94 thatdefine an outlet 96 for the compressed air. An outlet pre-diffusermid-point 98 is defined mid-way between the radially inner wall 92 andthe radially outer wall 94 at the outlet 96.

The pre-diffuser 90 is arranged upstream of the lean burn fuel injectorhead 54 at a distance g (damp gap) from the meter panel 68. The damp gapg is defined as axial distance between the outlet pre-diffuser mid-point98 and the meter panel mid-point 69. The pre-diffuser 90 is distancedfrom the combustor chamber 60 such that the ratio g/d of the damp gap gto the lean burn fuel injector head tip diameter d may be less than1.30, for example less than 1.15, and greater than 0.65, for examplegreater than 0.85. In an embodiment, the combustor chamber 60 may have aratio g/d of 1.05.

Arranging the pre-diffuser 90 at a distance to the meter panel 68 suchthat the ratio g/d of the damp gap g to the lean burn fuel injector headtip diameter d may be less than 1.30 and greater than 0.65 may furtherimprove the aerodynamics of the pilot and main fuel and air mixturewithin the combustor chamber 60, and in particular within the primarycombustion zone 80.

Although the present disclosure has been described with reference to aturbofan gas turbine engine it is equally possible to use the presentdisclosure on a turbo-jet gas turbine engine, a turbo-shaft gas turbineengine or a turbo-prop gas turbine engine. Although the presentdisclosure has been described with reference to an aero gas turbineengine it is equally possible to use the present disclosure on a marinegas turbine engine, or an industrial gas turbine engine.

We claim:
 1. A lean burn combustor comprising: a plurality of lean burnfuel injectors, each comprising a fuel feed arm and a lean burn fuelinjector head with a lean burn fuel injector head tip, wherein the leanburn fuel injector head tip has a lean burn fuel injector head tipdiameter (d), the lean burn fuel injector head comprising a pilot fuelinjector and a main fuel injector, the main fuel injector being arrangedcoaxially and radially outwards of the pilot fuel injector; and acombustor chamber extending along an axial direction and comprising aradially inner annular wall, a radially outer annular wall, and a meterpanel provided upstream of the radially inner and radially outer annularwalls with a plurality of apertures adapted for accommodating the leanburn fuel injector head tips, the radially inner annular wall, theradially outer annular wall, and the meter panel defining the size andshape of the combustor chamber, wherein the combustor chamber has acombustor chamber length (L) and comprises a primary combustion zonewith a primary combustion zone length (Z) and a primary combustion zonedepth (D), and a secondary combustion zone with a secondary combustionzone length (L-Z) arranged downstream of the primary combustion zone;wherein a ratio D/d of the primary combustion zone depth to the leanburn fuel injector head tip diameter is less than 2.4, and wherein aratio Z/d of the primary combustion zone length to the lean burn fuelinjector head tip diameter is less than 1.40.
 2. The lean burn combustorof claim 1, wherein the ratio D/d of the primary combustion zone depthto the lean burn fuel injector head tip diameter is less than 2.0. 3.The lean burn combustor of claim 1, wherein the ratio D/d of the primarycombustion zone depth to the lean burn fuel injector head tip diameteris greater than 1.2.
 4. The lean burn combustor of claim 1, wherein aratio L/D of the combustor chamber length to the primary combustion zonedepth is less than 2.0.
 5. The lean burn combustor of claim 1, wherein aratio L/D of the combustor chamber length to the primary combustion zonedepth is greater than 1.0.
 6. The lean burn combustor of claim 1,wherein a ratio L/d of the combustor chamber length to the lean burnfuel injector head tip diameter is less than
 5. 7. The lean burncombustor of claim 1, wherein a ratio L/d of the combustor chamberlength to the lean burn fuel injector head tip diameter is greater than1.5.
 8. The lean burn combustor of claim 1, wherein the radially outerannular wall of the combustor chamber forms an outer angle α_(outer)with the axial direction, the outer angle α_(outer) being comprisedbetween 0° and 15°.
 9. The lean burn combustor of claim 1, wherein theradially inner annular wall of the combustor chamber comprises a firstpart and a second part, the second part forming an inner angle α_(inner)with the first part, the inner angle α_(inner) being comprised between15° and 50°.
 10. The lean burn combustor of claim 1, wherein the leanburn fuel injector head generally extends along a longitudinaldirection, the longitudinal direction forming a cant angle with theaxial direction, the cant angle being comprised between 0° and 10°. 11.The lean burn combustor of claim 1, wherein the radially inner annularwall, radially outer annular wall, and meter panel are each providedwith respective tiles, said tiles defining respective inner surfaces ofthe radially inner annular wall, radially outer annular wall, and meterpanel.
 12. A gas turbine engine comprising a lean burn combustor,wherein the lean burn combustor comprises: a plurality of lean burn fuelinjectors, each comprising a fuel feed arm and a lean burn fuel injectorhead with a lean burn fuel injector head tip, wherein the lean burn fuelinjector head tip has a lean burn fuel injector head tip diameter (d),the lean burn fuel injector head comprising a pilot fuel injector and amain fuel injector, the main fuel injector being arranged coaxially andradially outwards of the pilot fuel injector; and a combustor chamberextending along an axial direction and comprising a radially innerannular wall, a radially outer annular wall, and a meter panel providedupstream of the radially inner and radially outer annular walls with aplurality of apertures adapted for accommodating the lean burn fuelinjector head tips, the radially inner annular wall, the radially outerannular wall, and the meter panel defining the size and shape of thecombustor chamber, wherein the combustor chamber has a combustor chamberlength (L) and comprises a primary combustion zone with a primarycombustion zone length (Z) and a primary combustion zone depth (D), anda secondary combustion zone with a secondary combustion zone length(L-Z) arranged downstream of the primary combustion zone; wherein aratio D/d of the primary combustion zone depth to the lean burn fuelinjector head tip diameter is less than 2.4, and wherein a ratio Z/d ofthe primary combustion zone length to the lean burn fuel injector headtip diameter is less than 1.40.
 13. The gas turbine engine of claim 12,further comprising: an engine core comprising a compressor, the leanburn combustor, a turbine, and a core shaft connecting the turbine tothe compressor, and a fan located upstream of the engine core, the fancomprising a plurality of fan blades.
 14. The gas turbine engine ofclaim 13, wherein the compressor and turbine rotate about an engine mainrotational axis, the axial direction of the combustor chamber beingparallel to the engine main rotational axis.
 15. The gas turbine engineof claim 13, wherein the turbine is a first turbine, the compressor is afirst compressor, and the core shaft is a first core shaft; the enginecore further comprises a second turbine, a second compressor, and asecond core shaft connecting the second turbine to the secondcompressor; and the second turbine, the second compressor, and thesecond core shaft are arranged to rotate at a higher rotational speedthan the first core shaft.
 16. The gas turbine of claim 13, wherein thefan has a fan diameter greater than 220 cm and less than 420 cm.
 17. Alean burn combustor comprising: a plurality of lean burn fuel injectors,each comprising a fuel feed arm and a lean burn fuel injector head witha lean burn fuel injector head tip, wherein the lean burn fuel injectorhead tip has a lean burn fuel injector head tip diameter (d), the leanburn fuel injector head comprising a pilot fuel injector and a main fuelinjector, the main fuel injector being arranged coaxially and radiallyoutwards of the pilot fuel injector; and a combustor chamber extendingalong an axial direction and comprising a radially inner annular wall, aradially outer annular wall, and a meter panel provided upstream of theradially inner and radially outer annular walls with a plurality ofapertures adapted for accommodating the lean burn fuel injector headtips, the radially inner annular wall, the radially outer annular wall,and the meter panel defining the size and shape of the combustorchamber, wherein the combustor chamber has a combustor chamber length(L) and comprises a primary combustion zone with a primary combustionzone length (Z) and a primary combustion zone depth (D), and a secondarycombustion zone with a secondary combustion zone length (L-Z) arrangeddownstream of the primary combustion zone; wherein a ratio D/d of theprimary combustion zone depth to the lean burn fuel injector head tipdiameter is less than 2.4, and wherein a ratio Z/d of the primarycombustion zone length to the lean burn fuel injector head tip diameteris greater than 0.70.
 18. A lean burn combustor comprising: a pluralityof lean burn fuel injectors, each comprising a fuel feed arm and a leanburn fuel injector head with a lean burn fuel injector head tip, whereinthe lean burn fuel injector head tip has a lean burn fuel injector headtip diameter (d), the lean burn fuel injector head comprising a pilotfuel injector and a main fuel injector, the main fuel injector beingarranged coaxially and radially outwards of the pilot fuel injector; anda combustor chamber extending along an axial direction and comprising aradially inner annular wall, a radially outer annular wall, and a meterpanel provided upstream of the radially inner and radially outer annularwalls with a plurality of apertures adapted for accommodating the leanburn fuel injector head tips, the radially inner annular wall, theradially outer annular wall, and the meter panel defining the size andshape of the combustor chamber, wherein the combustor chamber has acombustor chamber length (L) and comprises a primary combustion zonewith a primary combustion zone length (Z) and a primary combustion zonedepth (D), and a secondary combustion zone with a secondary combustionzone length (L-Z) arranged downstream of the primary combustion zone;wherein a ratio D/d of the primary combustion zone depth to the leanburn fuel injector head tip diameter is less than 2.4, and wherein thelean burn combustor further comprises a pre-diffuser, arranged upstreamof the lean burn fuel injector head and adapted for providing thecombustor chamber with compressed air, the pre-diffuser being generallyannular and including radially inner and radially outer walls definingan outlet, a damp gap (g) being defined as an axial distance between amid-point between the radially inner and radially outer walls of thepre-diffuser at said outlet and a mid-point between the radially innerand radially outer annular walls of the combustor chamber at the meterpanel, wherein a ratio g/d between the damp gap and the lean burn fuelinjector head tip diameter is less than 1.3.
 19. The lean burn combustorof claim 18, wherein the ratio g/d between the damp gap and the leanburn fuel injector head tip diameter is greater than 0.65.